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Thread: Coating thickness variation

  1. #1
    Boolit Man
    Join Date
    Apr 2015
    Posts
    75

    Coating thickness variation

    I've been powder coating for several years, pistol calibers only. Also asbb, not spray gun. I tried hi-tek a month or so ago. Process is easier, but it takes just as long to get similar results due to multiple coats.

    One advantage I do see in hi tek is the film thickness uniformity. As the bullet seater interacts with the sides of the bullet, the oal is a function of coating thickness. Large variations in thickness will give larger variations in oal. Hi tek is significantly more uniform than powder in my experience.

    My 2 cents.

    Sent from my SM-G900V using Tapatalk

  2. #2
    Boolit Bub
    Join Date
    Dec 2017
    Posts
    50
    I agree thickness can vary if you don't use the same technique each time you powder coat using tumble method, Not to dismiss the HI-Tek coating but I have been able to Powder coat consistently the same thickness using the same method each time.

    I use a clear 3 litre rectangular clip top container and place 6 handfuls of cast bullets in each time regardless of calibre and add 3 of the largest Lee dipper of powder and with the top on rotate the container in 360 degree fashion until all the powder is on the bullets by this time the powder has mostly come off the container walls and then add another 1/2 lee dipper and repeat and look at the bullets and powder on the walls of the container, Im looking for when the powder stops sticking to the bullets and starts to sit on the bottom of the container and the walls of it then I stop adding powder and start cooking, I waste very little powder this way and my coating appears very uniform,

    Around my neck of the woods Humidity is always at least 45-85% and have never ever had a problem with powder not sticking year round so Im lucky I guess

    Cheers

  3. #3
    Boolit Master
    Dragonheart's Avatar
    Join Date
    Jan 2012
    Location
    Katy, Texas
    Posts
    2,040
    Quote Originally Posted by 10sandxs View Post
    I've been powder coating for several years, pistol calibers only. Also asbb, not spray gun. I tried hi-tek a month or so ago. Process is easier, but it takes just as long to get similar results due to multiple coats.

    One advantage I do see in hi tek is the film thickness uniformity. As the bullet seater interacts with the sides of the bullet, the oal is a function of coating thickness. Large variations in thickness will give larger variations in oal. Hi tek is significantly more uniform than powder in my experience.

    My 2 cents.

    Sent from my SM-G900V using Tapatalk
    There are equipment issues that affect OAL a lot more than the variation of PC. Typically a single coat will be 1-2 thousands, so are you getting larger variations in your coating?

  4. #4
    Boolit Master
    Join Date
    May 2016
    Location
    Putnam County, NY
    Posts
    742
    I was having trouble getting an even coat of PC with the shaking method but I didn't have the black BB's. After failing with the blue air soft BB's & not wanting to wait for the black ones I decided to try my HF double tumbler. I haven't looked back. It's even & effortless, I can coat about 8lbs in each tub in just a few minutes. I PCed & baked about 100lbs of 38's today.

  5. #5
    Boolit Man
    Join Date
    Apr 2015
    Posts
    75
    Quote Originally Posted by Dragonheart View Post
    There are equipment issues that affect OAL a lot more than the variation of PC. Typically a single coat will be 1-2 thousands, so are you getting larger variations in your coating?
    The last time I measured before sizing, yes, significantly larger than 1-2 thou, more like 2-5. Never gave it much thought till I was checking OAL when working up a new load. I size after coating so thought no big deal because your swaging to the right diameter on the bearing surface.

    I was getting large variations in OAL and it was driving me nuts. Even went back to the single stage to diagnose. Coated and uncoated bullets... bingo, we have our "winner". Uncoated seated fine, coated didnt.

    The math: assume a 30 degree angle (from vertical) where the seater plug contacts the sides of the bullet. It certainly varies, but as the angle decreases, the affect gets WORSE. Trigonometry tells us that for each 0.001 inch of coating thickness, you'll seat 0.002 inches lower (30-60-90 degree triangle). Now as both sides are coated, you have 2 "thicknesses" added, so the difference is doubled to 0.004" per 0.001" of coating variation.

    So, on a 30 degree taper, each 0.001" of variation could result in 0.004" of OAL change. If you have 0.003" of variation, you can get 0.012" of OAL variation which is significantly more that I would expect from reasonable quality reloading equipment.

    Coating method i use(d) is vibratory tumbler. Just cast about 1000 rounds so I may give powder another try, just verify.

    Sent from my SM-G900V using Tapatalk

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Abbreviations used in Reloading

BP Bronze Point IMR Improved Military Rifle PTD Pointed
BR Bench Rest M Magnum RN Round Nose
BT Boat Tail PL Power-Lokt SP Soft Point
C Compressed Charge PR Primer SPCL Soft Point "Core-Lokt"
HP Hollow Point PSPCL Pointed Soft Point "Core Lokt" C.O.L. Cartridge Overall Length
PSP Pointed Soft Point Spz Spitzer Point SBT Spitzer Boat Tail
LRN Lead Round Nose LWC Lead Wad Cutter LSWC Lead Semi Wad Cutter
GC Gas Check